This invention relates to liquid eutectic mixtures and more particularly, to liquid eutectic mixtures of lower alkyl esters of p-hydroxybenzoic acid such as isopropyl p-hydroxybenzoate, isobutyl p-hydroxybenzoate, n-butyl p-hydroxybenzoate, sec-butyl p-hydroxybenzoate and amyl p-hydroxybenzoate, and to methods of preparing such mixtures in situ with the components in the desired ratio to render the mixture liquid at room temperature.
As is known, p-hydroxybenzoic acid alkyl esters, such as isopropyl p-hydroxybenzoate, isobutyl p-hydroxybenzoate and n-butyl p-hydroxybenzoate, are useful as antimicrobial agents, for example, in the form of emulsions. Such esters have generally been used individually, are sparsely soluble in water and are usually solid at room temperature.
In U.S. Pat. No. 3,097,131, there are disclosed eutectic mixtures of esters of p-hydroxybenzoic acid which are liquid at room temperature and which are stated to overcome the drawbacks and inconveniences inherent in the conventional independent use of such esters. These mixtures are formed by mixing two or more independently prepared esters of p-hydroxybenzoic acid (e.g., n-butyl p-hydroxybenzoate, sec-butyl p-hydroxybenzoate and isobutyl p-hydroxybenzoate) and heating the mixture to melt and allowing the melt to cool to room temperature or by tritulating a mixture of such esters in a mortar at room temperature until the mixture melts.
However, heretofore, there has not been available practical means for forming room-temperature liquid eutectic mixtures of p-hydroxybenzoic acid alkyl esters in situ starting with p-hydroxybenzoic acid and the respective alcohols such as isopropyl, isobutyl and n-butyl, sec-butyl and amyl alcohols.